In no particular order, I would love to be a part of these! because their all just so awesome!!:

Uraboku (as someone important to Luka's younger brother, Luze)
Hakuoki (as an ally and good friend)
Brave 10 (as someone other than his gun, who Kakei-san falls in love with and as a close friend of Rokuro and Sasuke)
Shounen Onmyouji (as Kazane)
Neo Angelique Abyss (as an ally and good friend)
Amnesia (as a friend)
Vampire Knight (as someone who loves Ichiru or as Sara...reborned? to be with Takuma)
Tegami Bachi (as a lone traveler and then joined the Beehive)
Fairy Tail (formerly from Raventail moved to Fairytail after learning that being deceived of purpose)
Naruto (as my own character from the Mist Village but formerly from the Rain Village)
Bleach (would so let Kon have his share of hugs, seeing how everyone only puts him down and is to be by Grimmjow's side)
Yu Yu Hakusho (as an ally and good friend)
Digimon (digimon partner would be either or both Elecmon and Gazimon)
Pokemon (starter pokemon would be Mudkip)

((if Games count too))
Ninja Love (as the princess' daughter from the future)
Kingdom Hearts 358/2 Days (as Xion)
Final Fantasy XIII-2 (as Serah or her long lost twin sister Sarah)

Freaking the fate universe. Oooooo how I would kill to summon my own servant and fight alongside them. I want the Holy Grail!
I want to be a participant in the war. I would love the chance of being able to summon a magical, religious cup that grants wishes!

I think I would choose SAO because when I was big into FFXI I always wished it was a real world I could be whisked away to. I believe that I enjoyed SAO because certain things reminded me so much of the fun times I had playing FFXI

Very well worded black thunder, returning to my boring life after ending an anime does suck :/

But taking into consideration danger, fun and convenience, I think probably the world of Pokemon. But Fairy Tail would be my ideal choice if I could choose how Id be in that world. I mean there aren't any restrictions to catching Pokemon and succeeding there really, but not everyone can use Magic in Fiore so unless I knew for a fact I could be a wizard I wouldnt go x3

The uncensored and uncut version of classic Yu-Gi-Oh is my ultimate choice. I'm not very interested in the card game, though. I almost chose Digimon Adventure 1 and 2, but they're too kiddy. I'd have to worry too much about getting blown up in DBZ, as well. I like the idea of being in Fullmetal Alchemist Brotherhood, but the conspiracies are kind of crazy. The rest are either too crazy, too depressing, too kiddy, too lame, too frustrating, I can't adapt to them, or I don't know enough about them. The classic Yu-Gi-Oh is a nice balance of things, I have already researched miscellaneous details and characters associated with it, and it's decent similarities to reality means that I wouldn't have too much trouble with adjusting to it. I actually prefer the manga, but the subbed anime will have to do.
Also, I have no interest in taking over the role of an existing character, and I prefer to intermingle with the cast after the events of the anime takes place. I don't like the thought of corrupting the plot. At the most, I would play the part of a random bystander until the series "ends" in the eyes of anime viewers.